1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a method for fabricating an LCD having a liquid crystal dropping method applied thereto.
2. Discussion of the Related Art
Keeping pace with development of an information oriented society, demands on displays increase gradually in a variety of forms. Recently, to meet the demands, different flat display panels, such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), ELD (Electro Luminescent Display), VFD (Vacuum Fluorescent Display), and the like, have been under development, and some of which have been employed as displays in various apparatuses.
Although LCDs have been used most widely as mobile displays, the LCDs are replacing CRTs (Cathode Ray Tube) due to features and advantages of excellent picture quality, lightweight and thin design, and low power consumption. Besides mobile or portable displays, such as a monitor of a notebook computer, the LCDs are under development for TVs for receiving and displaying broadcasting signals, and monitors for computers.
Despite the various technical developments in the LCD technology in multiple fields, efforts for enhancing picture quality of the LCD as a display are inconsistent with the features and advantages of the LCD in some aspects. Therefore, for the LCD being employed in various fields as a general display, a key for development of the LCD lies on how much the LCD is needed to implement a high quality picture, such as high definition and high luminance, and a large sized screen, while still maintaining the beneficial features such as light weight and thin design and low power consumption.
The LCD is provided with a liquid crystal panel for displaying picture, and a driving part for providing a driving signal to the liquid crystal panel. The liquid crystal panel has first and second glass substrates bonded with a gap between the substrates, and liquid crystal injected between the first and second glass substrates.
The first glass substrate (a TFT array substrate), includes a plurality of gatelines arranged in one direction at fixed intervals, a plurality of datalines arranged in a direction perpendicular to the gatelines at fixed intervals, a plurality of pixel electrodes in respective pixel regions defined at crossed points of the gatelines and the datalines to form a matrix, and a plurality of thin film transistors switchable in response to a signal from the gatelines for transmission of a signal from the dataline to the pixel electrodes.
The second glass substrate (a color filter substrate) has a black matrix layer for shielding light from areas excluding the pixel regions, a (RGB) color filter layer for displaying colors, and a common electrode.
The foregoing first and second substrates are spaced apart by spacers, and bonded by a sealant having a liquid crystal injection opening, through which liquid crystal is injected.
The liquid crystal is injected by evacuating the space between the bonded two substrates and dipping the liquid crystal injection opening in a liquid crystal bath. The liquid crystal flows into the space between the two substrates by a capillary tube phenomenon. Once the liquid crystal is injected, the liquid crystal injection opening is sealed by a sealant.
However, the related art method for fabricating an LCD having liquid crystal injected therein has the following problems. First, the related art method has poor productivity because the dipping of the liquid crystal injection opening in a liquid crystal bath while the space between the two substrates are maintained at a vacuum takes much time. Second, the liquid crystal injection, particularly into a large sized LCD, can result in an imperfect filling of the liquid crystal in the panel, which is a cause of a defective panel. Third, the complicated and long fabrication of the liquid crystal injection process requires the use of many liquid crystal injection devices, which occupies much space.
Accordingly, a method of fabricating an LCD by using a liquid crystal applying method has been under research recently. A Japanese laid-open patent publication No. 2000-147528 discloses the following liquid crystal applying method.
A related art method for fabricating an LCD having the foregoing liquid crystal applying method will be explained with reference to FIGS. 1A–1F. Referring to FIG. 1A, UV sealant 1 is coated on a first glass substrate 3 having a thin film transistor array formed thereon to a thickness of approx. 30 μm, and liquid crystal 2 is applied on an inner side of the sealant 1 (a thin film transistor array part). No liquid crystal injection opening is provided in the sealant 3.
The first glass substrate 3 is mounted on a table 4 in a vacuum chamber ‘C’ which is movable in a horizontal direction. The entire bottom surface of the first glass substrate 3 is held by a first substrate holder 5 using vacuum.
Referring to FIG. 1B, an entire bottom surface of the second glass substrate 6 having the color filter array is held by vacuum at a second holder 7. The vacuum chamber ‘C’ is then closed and evacuated. The second holder 7 is moved down in a vertical direction until a gap between the first and second glass substrates 3 and 6 is 1 mm, and the table 4 with the first glass substrate 3 thereon is moved in a horizontal direction to pre-align the first and second glass substrates 3 and 6.
Referring to FIG. 1C, the second holder 7 continues to move down until the second glass substrate 6 comes into contact with the liquid crystal 2 or the sealant 1 on the first substrate 3.
Referring to FIG. 1D, the table 4 with the first glass substrate 3 thereon is moved in a horizontal direction to further align the first and second glass substrates 3 and 6.
Referring to FIG. 1E, the second holder 7 continue to move down until the second glass substrate 6 comes into contact with the sealant 1, if not already, and is pressed down until the gap between the second glass substrate 6 and the first glass substrate 3 becomes 5 μm.
Referring to FIG. 1F, the pre-bonded first and second glass substrates 3 and 6 are taken out of the vacuum chamber ‘C’, and a UV light 8 is directed to the sealant to set the sealant 1, thereby finishing the fabrication of the LCD panel.
However, the foregoing related art method for fabricating an LCD having the liquid crystal applying method has the following problems.
First, the sealant and liquid crystal are respectively coated and applied on the same substrate which takes more fabrication time before the two substrates are bonded.
Second, during the time needed for coating the sealant and applying the liquid crystal on the first substrate, no progress is made for the second substrate (i.e., the second substrate is idle while the first substrate is being processed), causing an unbalanced fabrication process between the first and second substrates, resulting in an inefficient operation of the production line.
Third, because the sealant and the liquid crystal are both placed on the first substrate, the first substrate with the coat of the sealant applied thereto cannot be subjected to cleaning by an ultrasonic cleaner (USC) because the sealant that is to bond the two substrates may also be cleaned away. Thus, unwanted particles remaining on the substrate cannot be removed, which may interfere with a proper contact of the sealant during bonding.
Fourth, since the two substrates are aligned as the liquid crystal or the sealant on the first substrate comes into contact with the second substrate, the orientation film on the second substrate may be damaged, subsequently resulting in a poor picture quality. Moreover, if the upper and lower tables or stages are not leveled, the first and second substrates may partially or unevenly come into contact with each other. This can scratch the patterns on the substrates and/or result in an uneven seal.
Fifth, the substrate alignment occurs twice by varying only the distance between the two substrates. This limits the accuracy of the alignment of the two substrates.
Sixth, as the substrates become larger, misalignment of the substrates are more likely to be caused during transfer of the substrates such as during substrate unloading or during a subsequent process after the substrates are bonded.
Seventh, as the substrates become larger, maintaining the pre-bonded state of the substrate until the sealant is set in a subsequent process becomes more difficult.
Eighth, the misalignment of the substrates may cause defective orientation of the liquid crystal due to liquid crystal flow between the substrates.
Ninth, the misalignment of the substrates may cause poor aperture ratio.
Eighth, a defective orientation of the liquid crystal may cause blots, such as from scratches, and blots related to luminance.